1. Field of the Invention
The present invention relates to a paper feed apparatus for sequentially transferring only an uppermost sheet out of sheets mounted on a paper feed tray in a stacked state at predetermined timing.
2. Description of the Related Art
There is proposed a paper feed apparatus of such a type as shown in FIG. 1. FIG. 1 is a schematic side elevational view of the proposed paper feed apparatus. A paper feed apparatus 100 includes a paper feed tray 102 for mounting many sheets 101 in a stacked state, primary paper feed device 103 for transferring only the uppermost sheet 101 on the paper feed tray 102, and secondary paper feed device 106 for transferring the sheet 101 transferred by the primary paper feed device 103 to a portion between a printing drum 104 and a press roller 105 at predetermined timing.
The primary paper feed device 103 includes a scraper roller 107 press-contacted with the uppermost sheet 101 on the paper feed tray 102, a stripper plate 108 arranged in the vicinity of the downstream side of the scraper roller 107, and a pickup roller 109 substantially press-contacted with the stripper plate 108. The scraper roller 107 and the pickup roller 109 are driven to rotate in the same direction by primary driving device (not shown). The secondary paper feed device 106 includes a pair of secondary paper feed rollers 110 arranged downstream of the primary paper feed device 103 in a sheet transfer direction, and a pair of guide members 112 and 113 providing a transfer path 111 between the members 112 and 113 in the vicinity of the paired secondary paper feed rollers 110. The paired secondary paper feed rollers 110 are driven to rotate by secondary driving device (not shown). The upper guide member 112 guides only the neighborhood of the secondary paper feed roller 110 and the upstream side of the upper guide member 112 in the sheet transfer direction is formed as an inclined section 112a directed upward.
With the above-described constitution, when the scraper roller 107 and the pickup roller 109 are rotated, the uppermost sheet 101 on the paper feed tray 102 is applied with a transfer force and thereby transferred, whereby a sheet 101 under the uppermost sheet 101 is also transferred by frictional resistance between the sheet 101 and the uppermost sheet 101. If the sheet 101 is transferred to a position at which the tip end of the sheet 101 enters between the stripper plate 108 and the pickup roller 109, a plurality of sheets 101 are dealt with the stripper plate 108 and the transfer of sheets 101 other than the uppermost sheet 101 is stopped at the stripper plate 108. At the same time, only the uppermost sheet 101 is transferred to a downstream side. When the sheet 101 thus transferred is guided by the guide member 113 and transferred to a position near the paired secondary paper feed rollers 110, the sheet 101 enters the transfer path 111 between the paired guide members 112 and 113. If the sheet 101 passes this transfer path 111, the tip end of the sheet 101 is introduced to the portion between the paired secondary paper feed rollers 110 and, as shown in FIG. 2, the transfer of the sheet 101 is stopped in a state in which the tip end side of the sheet 101 is slightly bent. Next, the paired secondary paper feed rollers 110 are rotated synchronously with the rotation of the printing drum 104. If the paired secondary paper feed rollers 110 are rotated, the sheet 101 which has been transferred to the portion between the paired secondary paper rollers 110 is applied with a transfer force and thereby transferred to the portion between the printing drum 104 and the press roller 105 at predetermined timing. The sheet 101 is transferred to the portion between the printing drum 104 and the press roller 105 while being press-contacted with the portion and printing is conducted to the sheet 101 in this press-contact transfer course.
Meanwhile, the paired guide members 112 and 113 introducing the tip end of the sheet 101 transferred by the primary paper feed device 103 to the portion between the paired secondary paper feed rollers 110 are set to have a constant distance h therebetween in the proposed paper feed apparatus.
However, if the distance h between the paired guide members 112 and 113 is set to be wide enough to allow a thick sheet to pass through the transfer path with a margin left, correction of sheet corrugation cannot be expected to be exerted to a thin sheet, a sheet with less flexibility or a largely corrugated sheet after being left for a while. As a result, the problem that the printed sheet 101 is wrinkled occurs. That is, as shown in FIG. 3, if the sheet 101 has a corrugated portion xe2x80x9caxe2x80x9d and passes between the paired secondary paper feed rollers 110 without correcting this corrugated portion xe2x80x9caxe2x80x9d, then the corrugated portion xe2x80x9caxe2x80x9d is crushed between the paired secondary paper feed rollers 110 and the sheet 101 has wrinkles xe2x80x9cbxe2x80x9d as shown in FIG. 4.
On the other hand, if the distance h between the paired guide members 112 and 113 is set to allow a thick sheet (including an envelope and the like) to pass between the paired guide members 112 and 113 narrowly, correction of sheet corrugation is expected to be exerted to a thin sheet, a sheet with less flexibility or a sheet corrugated after being left for a while. However, the problem that the thick sheet tends to clog occurs.
The present invention has been made to solve the above-described problems. It is, therefore, an object of the present invention to provide a paper feed apparatus which does not cause paper clogging when thick sheets are used and which does not generate wrinkles on sheets if thin sheets are used.
The first aspect of the invention provides a paper feed apparatus comprising: a paper feed tray for mounting a plurality of sheets in a stacked state; primary paper feed device for sequentially transferring only the uppermost sheet out of the sheets on the paper feed tray; a pair of secondary paper feed rollers arranged downstream of the primary paper feed device in a sheet transfer direction, and a pair of guide members providing a transfer path between the pair of guide members near the pair of secondary paper feed rollers; secondary paper feed device for introducing tip ends of the sheets transferred by the primary paper feed device by using the pair of guide members to a portion between the paired secondary paper feed rollers, and for transferring the sheets introduced to the portion between the pair of secondary paper feed rollers to a transport downstream side according to rotation of the pair of secondary paper feed rollers; and guide distance adjustment device for making a distance between the pair of guide members variable, wherein the guide distance adjustment device comprises an operation member operated by a user, and the guide distance adjustment device makes the distance between the pair of guide members variable by operating the operation member.
According to the first aspect of the invention, if the sheets are thick, the distance between a pair of guide members is set wide, thereby transferring the sheets to the transfer path between the paired guide members with a margin left. If the sheets are thin sheets, sheets with less flexibility or the like, the distance between the paired guide members is set narrow. By doing so, the sheets are subjected to correction of sheet corrugation at the time of passing through the transfer path between the paired guide members and then introduced to the portion between a pair of secondary paper feed rollers. Due to this, it is possible to prevent wrinkles derived from the pressurization of corrugated portions by the paired secondary paper feed rollers. Furthermore, a user can freely, arbitrarily change the distance between the paired guide members in light of the thickness of the sheets to be used or the like.
The second aspect of the invention provides a paper feed apparatus comprising: a paper feed tray for mounting a plurality of sheets in a stacked state; primary paper feed device for sequentially transferring only the uppermost sheet out of the sheets on the paper feed tray; a pair of secondary paper feed rollers arranged downstream of the primary paper feed device in a sheet transfer direction, and a pair of guide members providing a transfer path between the pair of guide members near the pair of secondary paper feed rollers; secondary paper feed device for introducing tip ends of the sheets transferred by the primary paper feed device by using the pair of guide members to a portion between the paired secondary paper feed rollers, and for transferring the sheets introduced to the portion between the pair of secondary paper feed rollers to a transport downstream side according to rotation of the pair of secondary paper feed rollers; and guide distance adjustment device for making a distance between the pair of guide members variable, wherein the guide distance adjustment device comprises a rotatably provided eccentric cam, and the guide distance adjustment device makes the distance between the pair of guide members variable according to a rotation position of the eccentric cam.
According to the second aspect of the invention, the distance between the paired guide members can be changed by eccentric cams either continuously or by stages.
The third aspect of the invention provides a paper feed apparatus according to the second aspect of the invention, wherein the primary paper feed device comprises a primary paper feed roller, the primary paper feed roller comprises a paper feed pressure variable operation member for changing paper feed pressure for pressing the sheets in the stacked state on the paper feed tray, and the primary paper feed roller drives the guide distance adjustment device in association with the paper feed pressure variable member, so that the distance between the pair of guide members is made variable.
According to the third aspect of the invention, if the sheets are thick, a paper feed pressure variable operation member is operated to set paper feed pressure high. If the sheets are thin, the paper feed pressure variable operation member is operated to set paper feed pressure low. By doing so, the distance between the paired guide members is made variable in association with this paper feed pressure variable operation member.
The fourth aspect of the invention provides a paper feed apparatus according to the second aspect of the invention, wherein the paper feed apparatus is constituted to detect a slide ratio of the sheets when transferring the sheets to the secondary paper feed device by the primary paper feed mans, to drive the guide distance adjustment device according to the detected slide ratio and to thereby make the distance between the pair of guide members variable.
According to the fourth aspect of the invention, if the sheets are thick, a high slide ratio is detected and if the sheets are thin, a low slide ratio is detected. The distance between the paired guide members is made variable in association with this slide ratio.